Method and system for cleaning fracture ports

ABSTRACT

A method of stimulating or cleaning a fracture port and the proximate well bore area, includes the steps of inserting a downhole assembly on coiled tubing into a production tubing string comprising a fracture port. The downhole assembly includes a fluid pulse generator and jetting tool which is positioned adjacent the fracture port, and fluid is pumped through the tool to create fluid pressure pulses and jet streams of fluid. The method and apparatus does not require isolating the fracture port to be cleaned with packers or seals.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the priority benefit of Canadian Patent Application 2,769,935 filed on Feb. 28, 2012 entitled “Method and System for Cleaning Fracture Ports”, the contents of which are incorporated herein by reference.

FIELD OF THE INVENTION

The present invention is directed to a method and system for cleaning out or stimulating fracture ports and the proximate wellbore area.

BACKGROUND

An oil or gas well relies on inflow of hydrocarbon products from the subterranean formation it intersects. Productive intervals may be left uncased (open hole) to expose porosity and permit unrestricted wellbore inflow of petroleum products. Alternately, the hole may be cased with a liner, which is then perforated to permit inflow through the openings created by the perforation.

Drilling deeper and horizontally into tighter reservoir rock has become more viable in many oil and gas bearing formations. However, it is still challenging to successfully complete these deeper oil and gas reservoirs using horizontal wells. When natural inflow from the wellbore is restricted, the wellbore may require treatment termed stimulation to enhance flow rates. This is accomplished by pumping stimulation fluids such as fracturing fluids, acid, cleaning chemicals or proppant laden fluids to improve wellbore inflow.

As drilling technology continues to exploit more complex and unconventional reservoirs, completion technology is being designed and developed to effectively stimulate multiple stages along a horizontal wellbore. The growth in multi-stage fracturing has been tremendous due to completion technology that can effectively place fractures in specific zones in the wellbore. By fracturing specific zones in the horizontal wellbore, there is a greater ability to increase the cumulative production in a shorter time frame.

In a conventional multi-stage fracture completion, fracture ports are intermittently placed along the horizontal wellbore, between open hole packers to create isolated fracture zones. Following a fracturing operation, it is often necessary to clean out and re-stimulate the fracture ports and proximate wellbore area, if they have become plugged or are suffering from wax, scale or asphaltene buildup. Proximate wellbore buildup of organic or inorganic scale and solids is referred to as skin damage in the industry. Conventionally, the cleaning of fracture ports and reversal of skin damage is done by isolating a portion of the production string including the fracture port using coiled tubing run isolation packers, and using fluid pressure and/or chemicals to stimulate or clean out the open fracture port.

However, it is a time-consuming process to place, set and unset the coiled tubing run isolation packers. Furthermore, the packers can fail to set and seal on the liner for a number of reasons including the presence of detritus materials like scale, corrosion, and metal and mechanical debris on the liner.

There is a need in the art for an alternative and efficient system and method of stimulating or cleaning fracture ports and the proximate wellbore area.

SUMMARY OF THE INVENTION

In one embodiment of the present invention it comprises a system for stimulating or cleaning a fracture port and the proximate wellbore area, comprising an assembly configured to be run on coiled tubing, the assembly comprising a fluid pulse generator and jetting tool, and not comprising an isolation packer or seal.

In one embodiment the fluid pulse generator and jetting tool comprises an elongate tool having a top jet sub, and a bottom jet sub, separated by a pulse generator. In one embodiment each of the top and bottom jet subs comprises a plurality of jetted openings distributed around the periphery of the top and bottom jet subs. In another embodiment, at least a portion of the jetted openings are angled away from the pulse generator.

In one embodiment the system further comprises a nose jet cone having a jetted opening. In one embodiment, the system further comprises a top reflective focusing chamber positioned between the top jet sub and the pulse generator and a bottom reflective focusing chamber positioned between the bottom jet sub and the pulse generator.

In one embodiment of the present invention it comprises a method of stimulating or cleaning a fracture port and the proximate wellbore area, comprising the steps of inserting a downhole assembly configured to be run on coiled tubing into a production tubing string comprising at least one fracture port, the downhole assembly comprising a fluid pulse generator and jetting tool, positioning the tool adjacent the at least one fracture port, and pumping fluid through the tool to create fluid pressure pulses and jet streams of fluid, wherein said method does not include a step of isolating the fracture port to be cleaned.

In one embodiment of the method, the fluid pulse generator and jetting tool comprises an elongate tool having a top jet sub, and a bottom jet sub, separated by a pulse generator.

In one embodiment of the method, each of the top and bottom jet subs of the tool comprises a plurality of jetted openings distributed around the periphery of the top and bottom jet subs. In one embodiment of the method, at least a portion of the jetted openings of the tool are angled away from the pulse generator.

In one embodiment of the method, the tool further comprises a nose jet cone having a jetted opening. In one embodiment of the method, the tool further comprises a top reflective focusing chamber positioned between the top jet sub and the pulse generator and a bottom reflective focusing chamber positioned between the bottom jet sub and the pulse generator.

In one embodiment of the method, the production tubing string comprises a horizontal section having a plurality of fracture ports, and the fluid pulse generator and jetting tool is advanced or retracted from fracture port to fracture port along the horizontal section.

In another embodiment of the method, the fluid pumped through the tool has a different chemistry as the tool is advanced from fracture port to fracture port, than when it is retracted from fracture port to fracture port. In one embodiment of the method, the fluid pumped comprises an acid, a surfactant, a solvent, or mixtures thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings, like elements are assigned like reference numerals. The drawings are not necessarily to scale, with the emphasis instead placed upon the principles of the present invention. Additionally, each of the embodiments depicted are but one of a number of possible arrangements utilizing the fundamental concepts of the present invention. The drawings are briefly described as follows:

FIG. 1 is a schematic side view of an oil and gas well having horizontal section and a multi-fracture port completion.

FIG. 2 is an exploded view of one embodiment of fluid pulse generator and jetting tool.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The invention relates to a method and system of treating a series of fracture ports in a wellbore using a fluid pulse generator and jetting tool. When describing the present invention, all terms not defined herein have their common art-recognized meanings. To the extent that the following description is of a specific embodiment or a particular use of the invention, it is intended to be illustrative only, and not limiting of the claimed invention. The following description is intended to cover all alternatives, modifications and equivalents that are included in the spirit and scope of the invention, as defined in the appended claims.

As used herein, a “a fluid pulse generator and jetting tool” means a tool which may be run into production tubing using coiled tubing, through which a fluid may be pumped. The tool comprises at least one jetted opening, and preferably a plurality of jetted openings, which emit a fluid stream at a relatively high velocity, and a fluid pulse generator which creates pressure pulses in the fluid stream. The fluid pulse generator may also be referred to as a fluidic oscillator.

In embodiments of the invention, a fluid pulse generator and jetting tool (100) is used to re-stimulate, or clean out fracture ports and the proximate bore hole area, by incorporating the tool in a wellbore stimulation assembly. The stimulation assembly may be a conventional horizontal wellbore (12) assembly which can be used to effect fluid treatment of a formation (10), and may include a tubing string (14) having a lower end (14 a) and an upper end extending to surface (not shown). Tubing string (14) includes a plurality of spaced apart ported intervals (16 a) to (16 e) each such ported interval having a plurality of fracture ports (17) opened through the tubing string wall to permit access between the tubing string inner bore (18) and the wellbore (12).

A packer (20 a) is mounted between the upper-most ported interval (16 a) and the surface and further packers (20 b) to (20 e) are mounted between each pair of adjacent ported intervals (16 a to 16 e), In the illustrated embodiment, a packer (20 f) is also mounted below the lower most ported interval (16 e) at the lower end (14 a) of the tubing string (14). The packers (20 a to 20 f) are disposed about the tubing string (14) and selected to seal the annulus between the tubing string (14) and the wellbore (12), when the assembly is disposed in the wellbore (12). The packers divide the wellbore (12) into isolated segments wherein fluid can be applied to one segment of the wellbore (12), but is prevented from passing through the annulus into adjacent segments. As will be appreciated the packers (20 a to 20 f) can be spaced in any way relative to the ported intervals (16 a to 16 e) to achieve a desired interval length or number of ported intervals per segment. In addition, packer (20 f) need not be present in some applications.

The packers (20 a to 20 f) may be of any construction, such as conventional solid body-type with at least one rubber or elastomeric packing element.

The fracture ports (17) may have a mechanism to open and close the openings, such as sliding sleeves (not shown in the figures). In the embodiment described herein, sliding sleeves are mounted over the fracture ports (17) to close them against fluid flow, but which can be moved away from their positions covering the fracture ports (17) to open them.

Conventionally, the stimulation assembly is run in and positioned downhole with the sliding sleeves each in their closed fracture port position. The sleeves are moved to their open position when the tubing string is ready for use in fluid treatment of the wellbore (12). Preferably, the sleeves for each isolated interval between adjacent packers are opened individually to permit fluid flow to one wellbore segment at a time, in a staged, concentrated treatment process. The sleeves may be actuated by use of a plug or ball inserted into the tubing string, which may be seated into a sealing position and activated by fluid pressure. A suitable apparatus is described in U.S. Patent Application No. 2011/0278010 A1, the entire contents of which are incorporated by reference herein (where permitted).

The tubing string (14) of the stimulation assembly is run into the wellbore and the packers (20 a to 20 f) are placed between the ported intervals (16 a to 16 e). If blast joints are included in the tubing string (14), they are preferably positioned at the same depth as the ported intervals. The packers are then set by mechanical or pressure actuation. Once the packers (20 a to 20 f) are set, stimulation fluids are then pumped down the tubing string (14). A ball or plug is pumped downhole to a seat (28) positioned at the lower end of the tubing string (14 a) to seal the end of the tubing string (14). Further balls or plugs are then pumped downhole to sequentially actuate the sliding sleeves, thereby opening the fracture ports (17) to allow fluid flow from the inner bore (18) of the tubing string (14) to the well bore and the proximate formation. The packers (20 a and 20 f) isolate fluid flow to the specific selected ported intervals. The process is continued until all desired segments of the wellbore (12) are stimulated or treated. When completed, the treating fluids can be either shut in or flowed back immediately.

The fracture ports (17) are left open to the formation, allowing ingress of production fluids. Over time, the fracturing ports (17) may plug or suffer from wax, scale or asphaltene buildup. Thus, it is often necessary or desirable to clean out or re-stimulate the fracture ports (17). Conventionally, this is done by isolating a portion of the production string (14) including the fracture port (17) using isolation packers run in the inner bore (18) of the tubing string (14), and using fluid pressure and/or chemicals to stimulate or clean out the open fracture port (17).

The applicants have unexpectedly found that a fluid pulse generator and jetting tool positioned within the tubing string (14) and adjacent a fracture port (17) may efficiently clean out a fracture port (17), without the need to isolate the ported interval. Therefore, the system of the present invention does not require an isolation packer or seal.

The fluid pulse generator and jetting tool (100) is a tool which generates fluid pressure pulses and a pressurized fluid stream. One embodiment of the tool (100) is adapted to be run into the wellbore on coiled tubing with a bottom hole assembly (not shown in the figures). The tool provides at least one, and preferably a plurality of jetted fluid streams, with a pressure pulse generator.

In one embodiment, the bottom hole assembly or BHA comprises an internal check valve (not shown) and attaches to the coiled tubing in a conventional manner. The bottom of the BHA threadingly engages the top of the top jet sub (104) in a conventional fluid-tight manner. The other components of the tool are fitted together in top to bottom order: a top reflective focussing chamber (106), a pulse generator (108), a bottom reflective focussing chamber (110), a bottom jet sub (112), and a nose jet cone (114).

Both the top jet sub and the bottom jet sub (104, 112) define a plurality of jetted openings (116), which preferably are angled towards the ends of the tool (100). In one embodiment, each of the top jet sub (104) and the bottom jet sub (112) comprises 6 jetted openings located around the periphery of each such sub.

The pulse generator (108) comprises an outer housing (120) and an internal generator (122) which defines at least one angled opening. Fluid under pressure which exits the internal generator (122) will cause the internal generator (122) to spin within the outer housing (120). The outer housing (120) defines at least one opening which periodically aligns with the angled opening of the internal generator (120) as the internal generator (122) spins within the outer housing (120). The pulse generator (108) attaches to the top reflective focussing chamber (106) and the bottom reflective focussing chamber (110) with top and bottom cross-overs (124, 126) respectively.

Each of the top and bottom reflective focussing chambers (106, 110) comprises an inner tube (130) which provides fluid communication between the top jet sub (104, 112) and the bottom jet sub and the pulse generator (108), and a slotted outer tube (132). The slotted outer tube (132) has an inside diameter which is slightly larger than the outside diameter of the inner tube (130), creating an annular space therebetween. The outer tube (132) defines a plurality of slots (133), which preferably are configured diagonally such the slot ends are farther away from the pulse generator (108) than the middle of the slots (133). The top and bottom reflective focussing chambers (106, 110) cause pressure pulses to propagate in the annular space between the inner and outer tubes (130, 132), and reflect back towards the pulse generator (108).

The bottom jet sub (112) is similar to the top jet sub (104) and comprises a plurality of jetted openings (116) which are preferably angled away from the pulse generator (108). The nose jet cone (114) is fitted to the bottom end of the tool (100), and may comprise a jetted opening (115), which is preferably aimed away from tool (100).

In use, the tool (100) is run into the production tubing (14) using conventional coiled tubing techniques and positioned adjacent to a fracture port (17) which is to be treated. Fluid is pumped under pressure through the coiled tubing and BHA. Upon reaching the tool (100), the fluid is jetted out the jet openings (116) in the top and bottom jet subs (104, 112), as well as the nose jet cone (114). The fluid also causes rotation of the internal generator (122) within the pulse generator (108) outer housing (120). When the angled opening of the internal generator (122) aligns with the angled opening of the outer housing (120), a pressure pulse is emitted from the pulse generator (108). As well, the pressure pulse is accompanied by a simultaneous pressure drop at all the jetted openings (116), resulting in a reverse pressure pulse through the jetted openings (116).

The fluid which is pumped through the tool (100) may comprise various chemistries designed to remove scale, wax or asphaltene build-up among other objectives, such as the breakdown of emulsions and dispersal of formation fines. For example, the fluid may comprise an acid, such as hydrochloric acid, which may facilitate dissolution of iron and calcium based scales. Organic acids or surfactants may also be effective. The fluid may comprise a solvent component which helps remove hydrocarbon components of the scale, such as wax or asphaltenes, and may help water wet the reservoir.

Because of the jet and pulse action of the tool (100), and the chemical action of the injection fluid, pressure isolation of the fracture port to be treated is not required. The jetted fluid and pressure pulses are effective in cleaning out the fracture port, so long as the tool is appropriately positioned adjacent the fracture port.

EXAMPLE

In one example, a tool configured as shown in the Figures was rigged onto coiled tubing and pressure tested. Once the pressure test was complete, the tool is run in hole at a run rate of about 25 m/min while clean brine was slowly pumped (50 l/min) into the tool to ensure the BHA and tool remain clean while running in hole.

Once near the tubing bottom, the brine fluid rate was increased to above 80 l/min and the run rate slowed to about 10 m/min. Fluid was then switched to a xylene solvent while the tool was run towards the toe, while attempting to locate the fracture ports using a collar locator and a measurement schedule.

Once at the toe, the tool is then slowly pulled out of hole, while locating the terminal fracture port. The fluid was then switched to acid while pulling out of hole. While in the vicinity of fracture ports, the acid was pumped at a high rate (>80 l/min) and was pumped at a lower rate (50 l/min) between fracture ports. The well was then shut in and the chemical was allowed to soak for a few hours.

As will be apparent to those skilled in the art, various modifications, adaptations and variations of the foregoing specific disclosure can be made without departing from the scope of the invention claimed herein. 

1. A system for stimulating or cleaning a fracture port and the proximate wellbore area, comprising an assembly configured to be run on coiled tubing, the assembly comprising a fluid pulse generator and jetting tool, and not comprising an isolation packer or seal.
 2. The system of claim 1 wherein the fluid pulse generator and jetting tool comprises an elongate tool having a top jet sub, and a bottom jet sub, separated by a pulse generator.
 3. The system of claim 2 wherein each of the top and bottom jet subs comprises a plurality of jetted openings distributed around the periphery of the top and bottom jet subs.
 4. The system of claim 3 wherein at least a portion of the jetted openings are angled away from the pulse generator.
 5. The system of claim 2 further comprising a nose jet cone having a jetted Opening.
 6. The system of claim 2 further comprising a top reflective focusing chamber positioned between the top jet sub and the pulse generator and a bottom reflective focusing chamber positioned between the bottom jet sub and the pulse generator.
 7. A method of stimulating or cleaning a fracture port and the proximate wellbore area, comprising the steps of inserting a downhole assembly configured to be run on coiled tubing into a production tubing string comprising at least one fracture port, the downhole assembly comprising a fluid pulse generator and jetting tool, positioning the tool adjacent the at least one fracture port, and pumping fluid through the tool to create fluid pressure pulses and jet streams of fluid, wherein said method does not include a step of isolating the fracture port to be cleaned.
 8. The method of claim 7 wherein the fluid pulse generator and jetting tool comprises an elongate tool having a top jet sub, and a bottom jet sub, separated by a pulse generator.
 9. The method of claim 8 wherein each of the top and bottom jet subs of the fluid pulse generator and jetting tool comprises a plurality of jetted openings distributed around the periphery of the top and bottom jet subs.
 10. The method of claim 9 wherein at least a portion of the jetted openings are angled away from the pulse generator.
 11. The method of claim 8 wherein the fluid pulse generator and jetting tool further comprises a nose jet cone having a jetted opening.
 12. The system of claim 8 wherein the fluid pulse generator and jetting tool further comprises a top reflective focusing chamber positioned between the top jet sub and the pulse generator and a bottom reflective focusing chamber positioned between the bottom jet sub and the pulse generator.
 13. The method of claim 7 wherein the production tubing string comprises a horizontal section having a plurality of fracture ports, and the fluid pulse generator and jetting tool is advanced or retracted from fracture port to fracture port along the horizontal section.
 14. The method of claim 7 wherein the fluid pumped through the tool has a different chemistry as the tool is advanced from fracture port to fracture port, than when it is retracted from fracture port to fracture port.
 15. The method of claim 14 wherein the fluid pumped comprises an acid, a surfactant, a solvent, or mixtures thereof. 